A fusing device to reduce lubricant leakage, includes a fusing belt having a heat source placed therein, a pressure roller placed to apply pressure to an outer surface of the fusing belt, and a nip plate to support an inner surface of the fusing belt so as to define a fusing nip between the fusing belt and the pressure roller. The nip plate includes a stepped portion spaced apart from the inner surface of the fusing belt so as to define a space for accommodation of a lubricant applied to the inner surface of the fusing belt. The fusing device may further include a side frame to rotatably support a longitudinal end of the fusing belt. The side frame may be provided with a lubricant guide to guide the lubricant on the longitudinal end of the fusing belt toward the center of the fusing belt.